Scalable camera traps for measuring the attractiveness of sugar baits to control malaria and dengue mosquitoes

Abstract

Background Attractive targeted sugar baits (ATSBs) are one of the new promising interventions that can complement existing vector control tools. However, there is need to provide reproducible and quantitative information on the level of attractiveness of ATSBs under field conditions. To do so, we customized camera traps for close-up imaging and integrated them into a rugged ATSB monitoring station for day and night-time recording of mosquitoes landing on the baits. Methods The camera traps were evaluated, in a semi-field system and then in the field in rural Tanzania. In semi-field 2m x 5m x 2m net chambers, the camera trap was set up to record mosquitoes landing on either an attractive sugar bait (ASB), a blank ASB or 20% sucrose (w/v). Next, 198 mosquitoes (33 males and 33 females of Anopheles arabiensis, Anopheles funestus and Aedes aegypti) were released into each chamber and allowed to seek a sugar-meal for 72h, with the camera recording images of mosquitoes present on the ASB at 1min intervals. In the field 16 camera traps were set in 16 households, 7 with ASB attractant, 7 with ASB blank and 2 with 20% sucrose (w/v). Human landing catch (HLC) was performed on the same nights as the camera trap recordings. Results Under the semi-field conditions, there were significantly more mosquitoes that visited the ASBs than the blank baits, with An. funestus visiting more frequently than An. arabiensis. There were no significant differences between females and male An. arabiensis visits, but female An. funestus visited more than their conspecific males. The duration of visits did not vary between the ASB and the blanks, nor between the mosquito species. Moreover, mosquitoes visited the ASB or sucrose equally, with An. arabiensis visiting the baits more than An. funestus. Female mosquitoes visited the baits more than the males. There was no significant difference in visit duration between all species. In the field study, a mean of 70 An. arabiensis were caught per person per night by HLC compared to 1 individual recorded per night on ASBs. There were significantly more visits by mosquitoes to the ASB than the ASB blanksand sucrose solution, with more An. arabiensisvisiting the baits than An. funestus or C. quinquefasciatus. Females of all species visited baits significantly more than males. Again, the duration of visits was similar between An. arabiensis, An. funestusand C. quinquefasciatus. Ae. aegypti very rarely visited ASBs in the semi-field experiments and none were observed on baits in the field. Conclusions The use of camera traps to record still images of mosquitoes present on ASBs provides robust, reproducible and quantitative information on their attractiveness under different environmental conditions. Therefore, camera traps are powerful tools for evaluating and improving the ATSB technology.